Which term describes the protein that carries oxygen in the blood?

• A. Coagulation factors
• B. Protein carrying oxygen
• C. Platelets
• D. Blood plasma

Answer: (B)

Oxygen transport in the blood is carried out by hemoglobin, a protein housed inside red blood cells. Hemoglobin has iron-containing heme groups that reversibly bind oxygen. As blood travels through the lungs where oxygen concentration is high, oxygen loads onto the iron to form oxyhemoglobin. In tissues where oxygen is scarce and carbon dioxide and acidity are higher, hemoglobin releases the oxygen where it’s needed. This cooperative binding makes oxygen uptake efficient and delivery precise.

The other options refer to components not responsible for carrying oxygen: coagulation factors are proteins involved in blood clotting, platelets are cell fragments that help form clots, and blood plasma is the liquid portion of blood that carries many substances but does not bind and transport oxygen like hemoglobin does.